Hi and welcome!

The K20D will autofocus down to EV -1 with the 50mm f1.4 lens. That's almost pitch black. I think the K10D is nominally the same.

But regardless of that the K20D is a leap forward in image quality, so I'd really urge you to upgrade at least to that. Substantially better? Yes.

Possibly this is dependent on the lens in use.

When I use a 50mm f1.7 or 50mm f1.4 I have no problems focusing, even in situations where it's so dark that it woul be hard to focus manually. In these situations the K20D is better than eyesight.

However, with a zoom that may end up at f5.6 at the long end the ability to focus in low light will be reduced.

What lens are you using when you experience focusing problems?

We could always look on the positive side instead of assuming the worst!

We could suppose that the price was so low because their large Pentax stock has lasted them for a while, but now the next batch is in and the price has had to jump upwards. Many computer systems will preserve the margin on a product so that when the cost price for an item increases the margin will be maintained, thus making a new selling price.

This is actually very good if it makes a direct relationship between what each unit actually cost and what we pay. It could lead to two prices if you bought two of the same item though.....

Very, very impressive images.

You're right or close enough to right Martin. I haven't checked at what point the L converter needs to be used, but the principle is as you say.

Good advice. When people give help it's often useful anyway to know where people are.

No point recommending a UK supplier to someone in the USA for example.

It's interesting to compare these with older lenses, as these newer ones are obviously largely plastic construction. The metal constructed lenses look amazing. So may bits....

Not to my knowledge. In the M series days there wasn't the same distinction as to budget lenses and pro ones as there is now.

It won't cost you very much and it's an excellent lens. There are quite a few 135mm lenses from Pentax but it's the Pentax Takumar (Bayonet) 135mm f2.5 that normally gets the "thumbs down" and even that one is not bad at all.